1. Field of the Invention
The present invention relates to a fluorescent marking composition and a fluorescent mark formed by said composition. More particularly, the present invention relates to a fluorescent marking composition which is excellent in dispersion stability, light resistance, heat resistance and water resistance, and a mark formed by said composition which does not bleed and has excellent light resistance, heat resistance and water resistance.
2. Description of the Related Art
In these years, information such as a company name or a trade name of a good is indicated by a bar code, and a bar code pattern is optically read to utilize such information for totaling sales amounts or analyzing distribution of goods.
Usually, the bar code is printed on a material by an ink jet printer and the like, and suitable for classifying and identifying the goods in a store or shop which deals with various kinds of goods.
Recently, many goods carry such bar codes. In addition, the bar code system is applied to controlling files, and the like. For example, the bar code system is applied in a mailing system in which mails are sorted by code controlling.
However, hitherto, the bar code is formed by printing black bars on a white substrate. Since this black-white bar code utilizes a difference of reflectance between the black bars and the white substrate for reading it, it has a drawback that it is hardly read when an area of a material on which the bar code is formed is stained. In addition, to read the black-white bar code, a reflected light should be in a visible wavelength region. Then, the black-white bar code may deteriorate appearance of the material carrying the bar code. For example, a bar code will damage a picture on a book cover, or a white surface of a post card.
As an improvement of a black-white bar code, a fluorescent mark, which is excited by ultraviolet ray and emits visible light, is used, or an infrared fluorescent bar code, which is excited by infrared ray and emits infrared ray, is used (Japanese Patent KOHYO Publication No. 500590/1994).
But, since the fluorescent mark which is excited by the UV ray and emits the visible light uses the visible light for reading the bar code, it still deteriorates the appearance of the material carrying the bar code. In addition, the bar code comprising such fluorescent composition is hardly read when an area of a material on which the bar code is formed is stained as in the case of the black-white bar code.
Since the infrared fluorescent bar code which is excited by infrared ray and emits infrared ray does not have the emission of the visible light, the presence of the bar code does not deteriorate the appearance of the material carrying the bar code, and the information of the bar code can be detected without significant influence by the stain on the bar code. The infrared fluorescent material comprises an infrared fluorescent dye which absorbs and emits light in an infrared wavelength range. When such dye is formulated as a marking composition and printed by an ink jet printer and the like on a substrate material having high absorbance of a liquid such as a marking ink, for example, Japanese paper, bleeding of the liquid composition, which is called as "feathering" occurs, whereby a read rate of the bar code is decreased, so that an apparatus which functions according to the information from the bar code tends to maloperate. In addition, a density of the information stored in the bar code is increasing, and a gap between adjacent bars is being decreased. Then, the feathering seems to be a fatal drawback of the bar code for increasing the information density of the bar code.
Since the conventional infrared fluorescent marking composition has a property to dye a substrate material which is an inherent property of the dye, the bar code printed by such composition is hardly read when the substrate material is one absorbing IR light, such as a black material. Further, since an organic dye contained in such marking composition has, in general, poor light and water resistance, it will be difficult to read the bar code due to fading of the bar code.
As the infrared fluorescent material, inorganic compounds comprising neodymium, yttrium, etc. may be used (cf. U.S. Pat. No. 4,202,491, Japanese Patent KOKAI Publication No. 9607/1978 and Japanese Patent Publication No. 22326/1979). However, since the inorganic fluorescent material has a long rise time to emit infrared light and long afterglow, an output from one mark overlaps an output from an adjacent mark when the marks are read at a high read rate, so that each mark cannot be identified.